The present invention relates to a system for detecting troubles of an intake system of an automotive engine.
A fuel injection system in which a basic fuel injection quantity is determined in accordance with pressure in an intake pipe and speed of the engine is used for automobiles. In such a system, if a trouble of the intake pipe, such as the coming out of a blind cap on the intake system at downstream of a throttle valve which is caused by backfire arises, the air is inducted in the intake pipe passing through a hole for the blind cap without passing the throttle valve. The pressure in the intake pipe rises with the inducted air. As a result, the fuel injection system operates to increase the basic fuel injection quantity in accordance with the high intake pipe pressure, which causes abnormal increase of the speed of the engine regardless of driver's intention.
Japanese Patent Application Laid-Open No. 58-214632 discloses a system for dissolving such a problem. The system stores reference data of intake pipe pressure determined by the opening degree of the throttle valve and the engine speed. Detected intake pipe pressure is compared with a stored pressure. If the detected pressure is higher than the stored pressure, the basic fuel injection quantity is fixed to a predetermined value, thereby preventing abnormal increase of the engine speed.
However, in an engine in which a bypass provided with an idle speed control valve (hereinafter called ISC valve) is provided around the throttle valve, the reference pressure dependent on the opening degree of the throttle valve and the engine speed does not coincide with the detected pressure because of air passing in the bypass. The system determines such a state as an abnormal state to fix the fuel injection quantity which is insufficient for the operating condition to reduce engine performance.